Time-averaged analysis and numerical modelling of the behavior of the multiphase flow and liquid lamella thickness inside an internal-mixing ACLR nozzle

The Air-Core-Liquid-Ring (ACLR) atomizer is an innovative internal-mixing pneumatic atomization technique, suitable for energy-efficient spray drying of highly viscous liquid feeds, with high solid contents. However, pneumatic atomizers such as the ACLR can suffer from unstable internal flow conditions, which may lead to a wide variation in the droplet diameter obtained. Therefore, the internal flow conditions of an ACLR-atomizer needs to be properly studied and comprehended. With that in mind, a computational fluid dynamic (CFD) model was implemented and tested with experimental data collected for different air pressures and liquid feed viscosities. The model used can predict average lamella thickness with a relative error of less than 10%, when compared to experimental results, although some degree of artificial dampening of the flow instabilities occurs at high viscosities and low pressures. These instabilities have to be investigated in more detail from both the numerical side, by further refining the CFD model to capture the moment-to-moment behavior of the flow, as well as on the experimental side, by studying the instability development at higher recording speeds.